1. Field of the Invention
The present invention relates to an apparatus for preoperative planning of an artificial knee joint replacement operation and a jig for supporting the operation in order to plan an artificial knee joint replacement operation for the knee of the human body using a tomographic image for medical use and perform the operation.
2. Description of the Related Art
In recent years, tomographic image diagnostic apparatuses such as X-ray CT scanners and MRI apparatuses have spread. The use of these apparatuses allows for the observation and diagnosis of parts of the body. In contrast, osteoarthritis of the knee has been increasing with aging not only in Japan but also in other countries. The operation in which the affected part of the knee joint is replaced with an artificial joint made of metal or ceramics is wide spread today. In the artificial knee joint replacement, the important consideration is that an artificial joint having the optimal shape and size for a patient is placed at the optimal angle and the optimal position.
As the operation planning for that, a template in which a two-dimensional shape of the artificial joint is drawn on a transparent film is superimposed on a simple X-ray image from the two-dimensional front and lateral side. Alternatively, the size, position, and orientation for placing the artificial joint as well as the extent and position of bone cutting are measured on the simple X-ray image film using a ruler at present.
In the manual measurement using the template and the ruler on the basis of the two-dimensional simple X-ray image, the measurement accuracy of the size and position is insufficient. In addition, it is difficult to figure out the installation position and the extent of bone cutting three-dimensionally and quantitatively. Therefore, considerable experience and accumulation of technique are needed.
Consequently, it has been difficult for all the orthopedists to immediately perform the exact and highly accurate operation planning and operation. Particularly, the accuracy as to the installation position and orientation of the artificial joint has a great effect on the durability of the artificial joint. In addition, the accuracy is the most important element to allow patients after the operation to go about their normal lives without ill effects every day for a long period of 10 or 20 years.
In the method using the two-dimensional template, it has been difficult to perform such processing.
On the other hand; in order to support an operator so that the operator can easily find an ideal bone cutting surface of the tibia in the artificial knee joint replacement, a technique which performs the three-dimensional simulation using the personal computer is considered as shown below (for example, Patent document 1: Jpn. Pat. Appln. KOKAI Publication No. 2004-008707).
Conventionally, when the installation angle of the component of the femur side (artificial joint) is determined during the operation, the method of using an alignment rod in the marrow (hereinafter referred to as a “rod in the marrow”) which is inserted into the bone is generally used. The angle of distal bone cutting surface which specifies the varus-valgus angle and the flexion-extension angle of the component is determined from a difference between the axis of the rod and the mechanical axis of the femur by inserting the rod in the marrow.
At this time, the angle of the rod in the marrow can be adjusted to target installation angle of the component to some extent with an instrument in determining the varus-valgus angle. However, the flexion-extension angle cannot be adjusted and is completely dependent on the insertion angle of the rod in the marrow. In other words, this means that the installation angle of the femur component is dependent on the insertion angle of the rod in the marrow.
In the method of using the rod in the marrow, since there are differences in the bone shape among individuals, the insertion angle of the rod in the marrow varies depending on each case. Thus, it is difficult to reliably form a distal bone cutting surface at a prearranged angle.
Further, the installation angle in the rotation direction of the femur component which is very important in clinical practice is determined in the distal bone cutting surface. Thus, when the distal bone cutting surface in itself is inaccurate, the rotation angle is inevitably inaccurate.
In this respect, there is no description about the failure caused by the use of the rod in the marrow at the femur side in Patent document 1 in which the technique at the side of tibia is described.